The United States' top infectious disease official on Monday hailed early results from Moderna's Covid-19 vaccine as "stunningly impressive," calling the result a validation for experimental mRNA technology that some had doubted.
"I had said, and I must admit, that I would have been satisfied with 70, or at the most 75 percent efficacy," he told AFP.
"The idea that we have a 94.5 percent effective vaccine is stunningly impressive. It is really a spectacular result that I don't think anybody had anticipated would be this good."
The physician-scientist leads the National Institutes of Health's National Institutes of Allergies and Infectious Diseases (NIAID), which began co-developing the vaccine in January, shortly after Chinese authorities disclosed the genetic sequence of the new coronavirus.
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The vaccine is based on a new technology that uses a synthetic version of a molecule called "messenger RNA" to hack into human cells, and effectively turn them into vaccine-making factories.
"There were many people who had reservations about using something that had not been tried and true over the years, in fact some people even criticized us for that."
On Monday, Moderna and the NIH announced their preliminary results based on 95 of the 30,000 volunteers they have recruited who fell ill with Covid-19.
Of the 95, 90 had been in the trial's placebo group, and five in the group that received the drug, called mRNA-1273, translating to an efficacy rate of 94.5 percent.
It follows a similarly impressive result from Pfizer-BioNTech last week, which reported an efficacy of 90 percent.
Asked whether it was too early to say if the mRNA platform had now been proven, Fauci, who is usually known for his cautious statements, said the jury was in.
"Oh no! I think when you have two vaccines, like this, that have proven to be greater than 90% effective, I think that mRNA is here, it's established itself, it doesn't need to prove anything anymore.
"The data speak for themself, it isn't me, it isn't my opinion, look at the data."
While Moderna has basked in the spotlight, Fauci was keen to highlight the critical work of the NIH, which he said was responsible for developing the correct "conformation" or spatial arrangement of the virus' spike protein, which the vaccine makes inside the body to elicit an immune response.
Looking forward, he said he was worried about anti-vaccine sentiment in the United States, the hardest-hit country in the world.
"There's a long way to go -- don't forget, you've got to get this distributed, you've got to get most of the people to get vaccinated.
"There's a lot of anti-vaccine sentiment in this country. You've got to overcome that and convince people to get vaccinated because a vaccine with a high degree of efficacy is of no use if nobody gets vaccinated."